The invention relates to a plant for producing cement, having a first stage for crushing raw material to form raw powder, a second stage for calcining and sintering the raw powder to form cement clinker, a third stage for cooling the sintered cement clinker, and a fourth stage for crushing the sintered cement clinker.
To produce cement from raw material, a mixture of known composition made of lime-containing rock as raw material firstly passes through a raw powder mill in a first stage, where the raw material is crushed to form raw powder. During the crushing, the raw material undergoes first drying and, in a following second stage, the raw powder is subjected to a heat treatment, firstly CO2 being expelled from the lime-containing rock, formally from the rock powder. Then, in the methods normally used, the rock powder de-acidified in this way is sintered in a rotary kiln, desired calcium silicate phases being formed at high temperature while sintering the individual raw powder particles. In a subsequent step, as third stage, the sintered material is cooled down suddenly in order firstly to feed the heat present in the sintered material back into the process but also to assist the silicate phase formation during quenching. The cooled cement clinker is then temporarily stored and, to produce cement, the cement clinker is ground with additives in a fourth stage to form fine cement powder.
Viewed overall, the cement clinker produced from the raw state as raw material as far as the finished cement passes through crushing at at least two points. Consequently, in a plant for producing cement, it is necessary to maintain at least two grinding installations, which possibly operate differently.
Furnishing different grinding systems requires high logistical effort. Not only is it necessary for different spare parts to be stocked but it is also necessary for the different grinding systems, which not infrequently originate from various providers, to be maintained with different aids and repaired in the event of damage. The necessary stoppage of the various grinding systems during maintenance or repair results in stoppage of the plant, as a result of which the operator must accept high stoppage costs.
In order to avoid the stoppages, it is known to furnish redundant grinding systems in order that these can replace one another when a grinding system is being maintained or repaired. This leads to overcapacity in grinding output in the plant, which is associated with high costs.